Remove bridge related code from the main codebase

[Paillat-dev]

Summary

Remove all code related to bridge from the main codebase to only have it in ext.bridge

What is the feature request for?

The core library

The Problem

Currently, you will find here and there in the codebase checks for compatibility with bridge-related things, or in general references to bridge feature, which always makes things over-complicated and unintuitive. Moreover, as an extension, bridge should not interfere with the main library, even if it is a "core extension".

The Ideal Solution

Refactor bridge for all of its code to be confined to ext.bridge. This will probably mean creating some kind of bridge.Cog, that subclasses Cog, and its respective metaclass to handle bridge commands registration.

The Current Solution

n/a

Additional Context

No response